1. Field
The invention relates to a process for the preparation of a masterbatch in the liquid phase of one or more diene elastomers, in particular a natural rubber latex, and of one or more fillers.
The term “masterbatch” is understood to mean an elastomer-based composite into which one or more fillers and optionally other additives has/have been introduced.
2. Description of Related Art
It is known that, in order to obtain the optimum reinforcing properties conferred by a filler in a tire tread and thus a high wear resistance, it is advisable generally for this filler to be present in the elastomeric matrix in a final form which is both as finely divided as possible and as homogeneously distributed as possible. In point of fact, such conditions can only be achieved in so far as this filler exhibits a very good ability, on the one hand, to be incorporated in the matrix during the mixing with the elastomer and to deagglomerate and, on the other hand, to disperse homogeneously in this matrix.
In point of fact, in order to improve the dispersibility of the filler in the elastomeric matrix, it is known to resort to a mixing of elastomer and filler in the “liquid” phase. In order to do this, recourse is had to an elastomer in the latex form and to an aqueous dispersion of the filler, commonly referred to as “slurry”.
The problem of the uniform dispersion of the fillers and in particular carbon black within the rubber had already been posed from 1955. Thus, there is known, from the document BE 541816, a process for the preparation of a masterbatch of rubber and of carbon black in the liquid phase. This process is carried out continuously and uses hydraulic impacts or intense mechanical stirring to bring about the dispersion of the carbon black within the elastomeric matrix.
Fillers other than carbon black can be used, such as silica.
U.S. Pat. No. 5,763,388 teaches a process for the preparation in the liquid phase of a masterbatch of a polymer latex and of silica as filler, comprising the incorporation within the latex of modified silica, that is to say silica which has reacted with a coupling agent. According to this document, this modification of the silica makes it possible to uniformly disperse the modified silica within the polymer latex.
The document WO 2010/011345 for its part discloses the hydrophobation of the silica in order to act on the scorch and the viscosity of the masterbatch obtained.
It emerges from these documents that it is difficult to control the homogeneity in the distribution of the fillers within the masterbatch, the limiting factor being related in particular to the coagulation phase, which is difficult to control.